Environmental Engineering Reference
In-Depth Information
69% to 80% during that time. A cohort of well-educated
pregnant women in Massachusetts reported consuming
less dark meat fi sh, canned tuna, and white meat fi sh after
publication of the FDA 2001 advisory (Oken et al., 2003).
Total fi sh consumption declined 1.4 servings per month
(about 17%) between December 2000 and April 2001, with
a further decline as of February 2002. An analysis using
data from the US Consumer Expenditure Survey found that
education and newspaper readership were associated with
reduced fi sh consumption after release of the national advi-
sory (Shimshack et al., 2005). A simulation study found that
reducing the total amount of fi sh consumed (e.g., to no more
than 12 oz/wk) was more effective at eliminating the high
end of the exposure distribution than changing the types of
fi sh consumed (Carrington et al., 2004).
Awareness of recreational fi sh consumption advisories in
the United States is generally low, ranging from 8% to 32%
(Anderson et al., 2004; Knobeloch et al., 2005; Gliori et al.,
2006). Furthermore, results from several surveys suggest
that awareness of recreational fi sh advisories is not more
common among higher-risk subgroups, such as pregnant
women, nor does awareness necessarily predict lower mer-
cury levels or less frequent consumption of higher-mercury
fi sh (Knobeloch et al., 2005; Silver et al., 2007; Karouna-
Renier et al., 2008; Burger and Gochfeld, 2009).
There have been several studies examining the infl uence
of national advisories in other countries. In 1998, authori-
ties in the Faroe Islands issued guidelines recommending
that pregnant and nursing women abstain from eating pilot
whale meat and blubber (Weihe et al., 2005). Of 1180 eli-
gible women, 415 responded to an initial survey and 270 to
a follow-up survey 1 year later. Mean hair mercury concen-
trations declined over the year in this responsive subset of
the population. In France, exposure to a fi sh advisory that
simultaneously addressed methylmercury risk and omega-3
fatty acid benefi ts led to a signifi cant decrease in total fi sh
consumption and exposure to mercury that was greatest in
children less than 6 years old (Verger et al., 2007). There was
no change in consumption of the most contaminated fi sh
listed in the advisory, which were rarely consumed.
It appears that messages that are simple, or targeted at
well-known fi sh species, are more likely to be effective.
In focus groups, participants preferred simple messages
(Nesheim and Yaktine, 2007). However, they did not always
respond appropriately to the messages. For example, almost
all participants reported that they would avoid species des-
ignated “Do not eat” regardless of whether or not they were
in the targeted audience. Presentation also matters; in a
survey of sport fi shermen, responses varied whether “risks”
or “benefi ts” were listed fi rst (Knuth et al., 2003).
There is concern that an unintended consequence of
promoting fi sh consumption advisories could be a reduc-
tion of intake in groups that are likely to benefi t from eat-
ing fi sh (Cohen et al., 2005; Mozaffarian and Rimm, 2006),
potentially having an overall detrimental impact on public
health. In addition to harmful contaminants, fi sh contains
a number of benefi cial nutrients, including protein, iodine,
and vitamin D, and it is the primary dietary source for long-
chain omega-3 fatty acids, including docosahexaenoic acid
(DHA) (Nesheim and Yaktine, 2007). DHA is a necessary
structural component of the brain and eye, and its develop-
mental benefi ts have been shown in some randomized tri-
als of supplementation during pregnancy and early infancy
(Hadders-Algra et al., 2007; Helland et al., 2003). Higher
DHA intake is also believed to be protective against cardio-
vascular outcomes such as stroke and sudden cardiac death,
so if groups at high risk for heart disease were to reduce their
intake of fi sh to avoid exposure to methylmercury, they
would also lose this potential benefi t (Cohen et al., 2005;
Mozaffarian and Rimm, 2006). Some jurisdictions, such as
New York City, have opted to promote more frequent con-
sumption of the fi sh lowest in mercury to counter the poten-
tial for reduction in fi sh consumption overall (New York City
Department of Health and Mental Hygiene, 2011).
Developing effective and benefi cial fi sh consumption
guidelines is a challenge (Hughner et al., 2008). Part of
the diffi culty lies in communicating the message with an
easy-to-understand conceptualization of the trade-offs
between benefi ts and risks (Nesheim and Yaktine, 2007).
There is also the challenge of synthesizing information
on co-occurring contaminants in fi sh (e.g., PCBs and con-
taminants associated with aquaculture) for which limited
data are available. Disagreement across federal agencies in
the United States, and among agencies within and outside
the United States, over what constitutes “safe” methylmer-
cury intake can confuse rankings of fi sh species into cat-
egories of recommended consumption frequency. The best
outcome would be expected if pregnant women and other
higher-risk populations substituted more-contaminated
with less-contaminated fi sh, while maintaining overall fi sh
intake at a level suffi cient to provide an adequate supply
of omega-3 fatty acids. For frequent fi sh consumers, this
may be diffi cult. However, there are a number of fi sh spe-
cies that are both high in benefi cial nutrients and low in
methylmercury (Figure 13.1) (Nesheim and Yaktine, 2007;
Mahaffey et al., 2008). It is encouraging that data for the
US population are now suggesting a shift toward consump-
tion of lower-mercury fi sh without a concurrent drop in
overall fi sh consumption (Mahaffey et al., 2009).
Conclusion
Mercury is an established toxicant with diverse exposure
sources. Methylmercury in fi sh is probably the most impor-
tant source of exposure worldwide because of its pervasive-
ness and neurotoxicity. However, the effects of low-level,
long-term exposure—and how these effects vary across
sensitive subgroups of the population—are still not well
understood. Ultimately, reducing health risks requires a
thorough understanding of the human contribution to
the release of mercury into the environment and a societal
commitment to control these releases.
